Der rote Apfel ist lecker.
English: The red apple is tasty.
Adjective declension in the nominative case means changing the ending of a German adjective when it comes before a noun in the subject position of a sentence.
Use adjective declension in the nominative when you describe the subject of a sentence with an adjective before the noun. The ending of the adjective depends on the gender (der/die/das), number (singular/plural), and the article (definite, indefinite, or none).
Der rote Apfel ist lecker.
English: The red apple is tasty.
Eine große Frau steht dort.
English: A tall woman stands there.
Das kleine Kind spielt.
English: The small child is playing.
Gute Freunde helfen immer.
English: Good friends always help.